CB FALCON MODBUS COMMUNICATION
Code Name Comment
0x01 ILLEGAL_FUNCTION
Illegal function code or
action requested
0x02
ILLEGAL_DATA_ADDRESS
Register address out of
bounds
0x03 ILLEGAL_DATA_VALUE
Data in register write is
invalid for register
0x10
READ_MULTIPLE_NOT_OK
Exceeded maximum
registers allowed in read
0x11 ACCESS_FAILURE
Invalid password access
level for register
0x12 LOGIN_FAILURE
Unrecognized password
given for login
16 (0x10) Write Multiple Registers
This function is used to write data into multiple Falcon
registers with a single request. The Falcon registers must be
located consecutively in the register map since only a base
address is provided. The Modbus master provides the
starting register address, the number of registers to write, and
the total number of bytes, followed by the actual data itself.
The Falcon writes the data into each register and
acknowledges the completion with a response echoing the
number of registers written.
When writing text data to a register representing variable
length text, the number of registers should be specified as one
and the byte count as the number of bytes in the text data.
17 (0x11) Report Slave ID
This function is used to locate and identify the Falcons
connected on the Modbus network. The Modbus master
issues a Report Slave ID request for a specific Modbus
address onto the Modbus network and if a Falcon with the
requested Modbus address exists, it responds to the request.
If none exists, the Modbus master times out and concludes
that no Falcon is present with that Modbus address.
Included in the Falcon response is the following data to
further identify it:
• OS number
• Burner name
The format of the Falcon response message is depicted in
Table 14.
Table 14. Report slave ID response
Byte: 0 1 2 3 4 5-20 21-40 41-42
Slave Address Function Code Byte Count Slave ID Run Indicator OS Number Burner Name CRC
0x01-0xF0 0x11 0x30 0x79 0x00=OFF
0xFF=ON
The OS number (up to 16 characters) and burner name (up to
20 characters) fields are NULL filled text strings. They have a
fixed field length so that the boundaries of each field are
known. These same Falcon parameters can be obtained with
the Read Holding Register function.
The Run Indicator status contains an OFF status when the
Falcon is in a lockout or unconfigured state. In any other case
the status indicates an ON condition.
NOTE: A slave ID of 0x79 is reserved for all Falcon
hydronic boiler control models at this time. Future
design may expand this list to include more IDs for
different models.
Exception Codes
The Modbus exception codes in Table 15 may be given by the
Falcon in response to function code requests.
Table 15. Modbus exception codes
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